Field of the Invention
The present invention relates to a sheath type heater or a sheath type temperature measuring sensor for performing heating or temperature measurement of fluid, solid and the like in various situations such as in piping, under the ground, or with a vacuum device. More specifically, the present invention relates to a coupling structure and a coupling method of a sheath structure assembly for coupling a plurality of sheath type heaters or sheath type temperature measuring sensors to one another in the axial direction, so as to extend the length.
Description of the Background Art
As the coupling structure of this kind, for example, the following coupling structure is proposed. A sheath type heater coupling structure includes: a tubular metal connector into which a heating wire projecting from a metal sheath end on the heating side and a non-heating wire projecting from a metal sheath end on the non-heating side are inserted; a coupling sleeve externally attached between the metal sheath ends; and a heat resistant insulator being interposed between the connector and the coupling sleeve. The opposite end portions of the coupling sleeve are fixed to the outer circumferential surfaces of the metal sheath ends through welding or brazing. Thereafter, the coupling sleeve is pressurized and deformed in the radially inward direction, to compress the heat resistant insulator. Thus, the connector is pressurized in the radially inward direction, so as to attach to the heating wire and the non-heating wire under pressure (see Japanese Unexamined Patent Application No. 2007-220325).
In connection with such a coupling structure, since it is not the structure in which the heating wire and the non-heating wire are abutted on each other and subjected to welding or silver brazing, but the structure in which the wires are attached on the metal connector under pressure to establish electrical connection, the length of the wires can be set relatively freely. Thus, the following effects are exhibited: an improvement in flexibility and a reduction in the cost of the coupling work can be achieved; a reduction in the strength of the connection portion and a reduction in the electrical connection attributed to thinning or a hollow can be avoided; and a uniform and excellent electrical connection can be obtained. Further, it is the structure in which the heat resistant insulator is interposed between the connector and the coupling sleeve, and the coupling sleeve is pressurized and deformed in the radially inward direction, whereby the heat resistant insulator is compressed and the connector is simultaneously pressurized in the radially inward direction, so as to be attached to the heating wire and the non-heating wire under pressure. Therefore, the following effects can also be exhibited: joining of the wires and compression of the insulator can simultaneously be performed efficiently; the heat resistant insulator can easily obtain the uniform high packing density similarly to that of the insulating powder in the metal sheath of the heating portion; and break or a reduction in insulating performance attributed to usage can be prevented.
However, for example, in the case where the coupling structure is used as being arranged in piping, under the ground, or in a structure extending over the distance as great as several thousand meters or more, or in the case where a fluid whose flow velocity or viscosity is very great or a solid with great vibration is subjected to heating or temperature measurement, a great force such as tension, compression, twist, or shock continuously occurs at the coupling portion. In particular, durability of the welded portions between the coupling sleeve opposite end portions and the metal sheath outer circumferential surface may be impaired. Provided that the welded portions are impaired, sealability will be reduced even if damage or break does not occur. This invites a reduction in insulating performance attributed to intrusion of humidity.
Accordingly, in consideration of the circumstances described above, the present invention is directed to provide a sheath structure assembly coupling structure and a sheath structure assembly coupling method, which exhibit excellent workability, achieve a reduction in costs, and avoid a reduction in the strength of the connection portion or in the electrical connection. Further, such coupling structure and coupling method can achieve uniform and excellent electrical connection, maintain excellent durability for a long period and prevent break or a reduction in insulating performance even in the usage environment where a great force such as tension continuously acts.